Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $192.53   13.413%   $218.354   $218.35   $218.35   $218.40  
  Purchase #2 $208.87   10.578%   $230.9643   $230.96   $230.95   $231.00  
  Purchase #3 $160.30   9.738%   $175.91   $175.91   $175.90   $175.90  
  Purchase #4 $96.57   7.721%   $104.0262   $104.03   $104.05   $104.00  
  Purchase #5 $163.38   11.233%   $181.7325   $181.73   $181.75   $181.70  
  Purchase #6 $248.86   3.635%   $257.9061   $257.91   $257.90   $257.90  
  Purchase #7 $113.27   12.133%   $127.013   $127.01   $127.00   $127.00  
  7 purchase totals = $1,183.78       $1,295.9061   $1,295.90   $1,295.90   $1,295.90